YELLOWKNIFE – Federal officials are scrambling to clean up a crumbling, abandoned northern gold mine that is in imminent danger of releasing massive amounts of arsenic, asbestos and other toxins.

“It’s pretty scary stuff,” said Mark Palmer, senior adviser on Aboriginal Affairs and Northern Development’s Giant Mine Project, which describes a proposed cleanup of collapsing, poison-filled buildings and caverns on the shore of Great Slave Lake as an emergency response.

“We are worried they are going to fall down and if that happens there will be a release.” The Giant Mine just outside Yellowknife was an economic mainstay for 50 years. But its gold was locked within crystals of arsenopyrite, and after the mine finally closed in 2004, about 237,000 tonnes of highly toxic, water-soluble arsenic trioxide remained on the site.

Most of the arsenic was blown back underground, where huge dustpiles of it sit in 15 subterranean chambers, some big enough to swallow an 11-storey building. About 3,600 cubic metres of arsenic and arsenic-contaminated material remain in surface structures — uncontained and, in many cases, exposed to the elements.

A $488-million plan to clean up the site and freeze the underground arsenic in place — Canada’s biggest environmental cleanup — is before northern environmental regulators.

But engineering reports say the buildings and some of the underground caverns have deteriorated so badly that the cleanup must begin as soon as possible to contain various poisons, which also include mercury, cyanide and PCBs.

“Many of the underground elements are showing signs of failure, including the formation of a sinkhole at the surface,” says the department’s application for the emergency cleanup.

“There is the potential for significant impacts to the environment and injury to humans through falling cladding, partial building collapse and arsenic and asbestos exposure to humans and wildlife.”

Arsenic poisoning starts with headaches, confusion, severe diarrhea and drowsiness. When the poisoning becomes acute, symptoms may include diarrhea, vomiting, blood in the urine, cramping muscles, hair loss, stomach pain and more convulsions.